1. Field of the Invention
The present invention relates to a method and apparatus for probing a component using a numerically controlled device, and, more particularly to a method and apparatus for probing specific features on a component to determine their pattern on the component.
2. Background Information
The present invention relates to a Numerically Controlled (NC) device. As shown in FIGS. 1a and 1b, an NC device 400 often includes a platform 402 which uses support devices, shown here as stand-offs 404a-c, to hold a component 406 in a fixed position. The NC device 400 also has a chuck 408 attached to an articulating head 410 capable of pivoting about a "b" axis, as shown in FIG. 1a, as well as an "a" axis and a "c" axis, as shown in FIG. 1b. The NC device 400 moves the chuck 408 along the X-axis and the Y-axis utilizing movement of an arm 412 that travels along tracks (not shown). The chuck 408 can be repositioned along the X axis and the Y axis allowing the formation of a plurality of features, some of which can be positioned on the component 406 in a predetermined pattern. The arm 412 is also capable of moving the position of the chuck 408 along the Z-axis using a vertical track 414, shown in FIG. 1b. The chuck 408 may hold a drill, a milling tool, as well as a number of other tools typically used in precision machining. Accordingly, the NC device 400 is capable of performing a machining operation at a number of positions on the component 406 to form a predetermined pattern.
As shown in the block diagram of FIG. 2, the NC device 400 includes an input device 416 for inputting "high level" instructions designating the precise locations for machining each of the features, including those of a pattern, on the component 406. These instructions are transmitted to a post processor 418. The post processor 418 is in communication with a machine control unit (MCU) 422 of the NC device 400. The post processor 418 adapts the "high level" instructions of the input device 416 to the specific requirements of the NC device 400 and its MCU 422, and outputs a work piece instruction understandable to the MCU 422. The instructions from the post processor 418 are stored in a memory 420. The memory 420 can either be part of the NC device 400, as is the case when the NC device 400 is a computer numerical control (CNC) device having its own dedicated individual computer, or the memory 420 can be located remote from the NC device 400, as is the case when the NC device 400 is a direct numerical control (DNC) device. In the case where the NC device 400 is a DNC device, a remote computer such as a mainframe or UNIX.RTM. workstation will hold the instructions from the post processor 418 in a separate memory until accessed by the MCU 422.
To operate the arm 412 and the articulating head 410 of the NC device 400, shown in FIG. 1a, the MCU 422 sequentially accesses work piece instructions from the memory 420 and then translates these instructions into signals directly actionable by the NC device 400. For example, if the instruction is to move the chuck 408 to a first hole location of a predetermined pattern at a position some n number of units along the X-axis, then the MCU 422 will apply a voltage to at least one of motors 424a-424e to drive the arm 412 along the track (not shown) on the platform 402, until it has moved the designated number of n units. In an open loop system, a known amount of travel will be performed by the motors 424a-424e, preferably stepping motors, when a given voltage for a given duration is applied to the motors 424a-424e. On the other hand, in a closed loop system, the MCU 422 will apply the signal voltage until a sensing device (not shown) determines that the arm 412 has traveled the designated number of units. Thus, in a closed loop system, the articulating head 410 moves in response to instruction from the MCU 422 and then the sensing device (not shown) indicates to the controller 422 when the desired position has been reached.
The movement of the chuck 408 some n number of units along the Y-axis is accomplished by the MCU 422 in the same manner as was the X-axis. Once the position of the first hole has been located along the X-axis and the Y-axis the MCU 422 applies a voltage to at least one of the motors 424a-424e to drive the chuck 408 along the vertical track 414 to a desired depth within the component 406. The MCU 422 repeats this process for each feature in the pattern.
Once the NC device 400 has completed a plurality of operations to form various features within the component 406, including the formation of at least one predetermined pattern, the accuracy of each of the operations must be checked. Then, the predetermined pattern formed on the component 406 must be compared with the composite tolerances of the pattern to determine if the pattern was formed within acceptable limits.
One method of ensuring that the features, as well as the predetermined pattern, machined on the component 406 are in tolerance is to remove the component 406 from the stand-offs 404a-404c and transfer the component 406 to a coordinate measurement machine (CMM) (not shown). However, when the component 406 is large, such a transfer becomes exceedingly difficult and may cause the component 406, and thereby the pattern on the component 406, to permanently distort by warping or drooping. Further, the CMM tends to be expensive to purchase and operate, so there are usually only a few available at a manufacturing facility. This causes long queues and delays before the component 406 can be checked. When using the CMM (not shown) to determine if a pattern on the component 406 is within tolerance, an offset is chosen to compensate for machining variations and axial differences before comparing ideal pattern dimensions with measured pattern values. Once the offset has been determined, each feature is sequentially probed, and then the dimensions and center of the feature are calculated. The data indicating the center of each feature are then offset by the amount chosen. The features in the ideal pattern as offset are then compared with the measured pattern values. If one of the features, such as a hole, is found to be out of tolerance, then a new offset is chosen, and the CMM probes each hole all over again. The center values of the new probing are then offset with the new value to determine if the pattern is in tolerance. This lengthy procedure is repeated over and over until all features are found to be tolerance or until all reasonable offset values have been tried. Thus, if the first few offsets calculated lead to poor tolerance measurements of at least one of the features, then each time a new offset is calculated, every single feature in the pattern on the component 406 must be physically re-measured. Further, if every attempt to obtain acceptable tolerances using different offsets fails, the CMM has no way to determine which offset yielded the best results, i.e., the offset yielding the least number of features in the pattern that were out of tolerance.
For the foregoing reason, there is a need for an apparatus and a method that can determine if a pattern machined onto a component is within tolerance without requiring the resampling of data once it has been acquired. Further, the apparatus and method should provide the best pattern data available, even if some features of the pattern are out of tolerance. The probe technology should accomplish the above objectives by utilizing a plurality of data to determine if the component 406 is acceptable. Finally, the apparatus and method should allow the probing of the component 406 to be conducted by the NC device that machined the component, to forego the delays and distortions caused when the component is transferred to a CMM.